Conventionally, semiconductor memories are classified into a volatile memory and a non-volatile memory. The volatile memory generally includes a RAM (Random Access Memory) such as a DRAM (Dynamic RAM) or a SRAM (Static RAM). Data may be written and stored in the volatile memory during applying a power supply but the data are volatilized therefrom if a power supply is shut off, thereby losing the data. On the contrary, the non-volatile memory, e.g., a ROM (Read Only Memory) stores data therein even though a power supply is not applied.
Non-volatile memories are divided into floating gate series and MIS (Metal Insulator Semiconductor) series depending on a processing technique. In the MIS, two or more kinds of dielectric films are multi-layered in double or triple layers.
The memory of the floating gate series stores data therein by using a potential well. Such memory of the floating gate series is represented by an ETOX (EEPROM (Electrically erasable programmable read only memory) Tunnel Oxide) structure widely employed as a flash EEPROM.
The memory of the MIS series stores data therein by using traps existing in a dielectric film bulk, an interface between two dielectric films and an interface between a dielectric film and a semiconductor. Such memory of the MIS series is represented by a MONOS/SONOS (Metal ONO Semiconductor/Silicon ONO Semiconductor) structure usually employed as a flash EEPROM.
With the development of the processing techniques, a SOC (System-on-Chip) technique is required and the importance thereof becomes a prominent figure. The SOC technique is referred to techniques capable of performing various functions on a single chip, i.e., basic Logic, SONOS and Flasys. However, such techniques involve too complicated processes.